Electrolytic reduction of sugars



Patented May 16, 1950 ELECTROLYTIC REDUCTION OF SUGAR/S Hans Rudolf Hefti and Werner Kolb, Zurich, Switzerland No Drawing. Application October 27, 1948,

Serial No. 56,904 8 Claims. (01. toi -i7) The invention relates to an improved method and process'for the electrolytic reduction of reducible varieties of sugarrsuch as for example glucose, galactose, lactose and xylose-to polyhydric alcohols in an undivided electrolytic cell not supplied with a diaphragm.

The commercial reduction of glucose to sorbitol and mannitol in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm is well known and has become a process of technical importance. However, the hitherto existing necessity to employ a diaphragm for separating the anolyte from the catholyte in the electrochemical reduction of sugars to polyhydric alcohols is a serious disadvantage.

By the insertion of a diaphragm the conduction resistance to the passage of the current through the cell is considerably increased. The ;rapid alteration of the original permeability of :the diaphragm necessitates its exchange after ;.a short useful life. In addition thereto the man- ;ufacture of eflicient diaphragms, effecting a surfiicient separation of the anolyte from the cathrolyte, possessing satisfactory mechanical properities, and resistant to the chemical influences of .the electrolytes, is difficult. For such reasons the diaphragm increases the operating costs of the cell, raises the current consumption, and lowers the yield.

Protracted investigations relating to means for preventing the oxidizing efiect of the nascent roxygen at the anode from exerting a deleterious iinfiuence on the sugar reduced at the cathode without the employment of a permeable diaphragm i. e. in a simple electrolytic cell with a common electrolyte both for the cathode and the :anode, supplied results which form the basis of the method and process according to the invention. We found that a deleterious influence of the anodic oxidation on the cathodic reduction products can be substantially prevented by the addition of a wateresoluble inorganic sulphite to the sugar solution.

With the maintenance of a surplus of sodium sulphite or of ammonium sulphite in an aqueous solution of glucose showing an alkaline reaction, it proved possible to carry out the reduction to sorbitol and mannitol without any difiiculty in a simple cell without a diaphragm at room temperature and the yield was very satisfactory. In the same manner a purified solution of the wood sugar xylose can be reduced to xylite, and the other reducible sugars can be reduced to the corresponding polyhydric alcohol.

The method and process according to the invention for the electrolytic reduction of sugars to polyhydric alcohols is substantially characterized in that'a reducible'sugar in aqueous solution with the addition of a water-soluble inorganic sulphite is submitted to a cathodic reduction in a simple electrolytic cell without a diaphragm, and this in such manner that the sulphite is converted into the corresponding sulphate and the anodic oxidation of the obtained reduction products is eiiectively prevented by maintaining a surplus of sulphite in the electrolyte.

For the reduction of glucose an alkaline reaction of the electrolyte is particularly favourable and this can be obtained by the addition of a commercial grade of sodium sulphite containing a certain quantity of soda, Alkalization of the electro-.- lyte can be further accomplished by the addition of the hydroxide corresponding to the employed sulphite, in this case, sodium hydroxide.

The electrolytic cell may consist of glass or stoneware, but for larger units a rubber-lined equipment is preferable. The cathode can be made of zinc, lead, cadmium, cadmium-zinc alloys, amalgamated zinc, lead, or cadmium. Furthermore pure mercury may be employed as cathode. Experiments showed that not only the material of the cathode is important, but also the shape. Ribbed cathodes of large surface or such consisting of a diminutive suitable material are particularly advantageous. Mercury containing cathodes have the advantage to form both with sodium and ammonium readily decomposable amalgams which develop hydrogen.

The anode may consist of lead or graphite.

Both the reduction of the sugars and the oxidation of the employed sulphite can be promoted by the addition of suitable catalysts to the electrolyte.

The method and process according to the invention is illustrated by the following example without restricting the scope of the invention.

Example 150 g. of pure glucose and 120 g. of sodium sulphite were dissolved in 1000 0.0. of Water. The obtained solution showed an alkaline reaction and was treated in a simple electrolytic cell supplied with a cathode made of amalgamated lead and a graphite anode with a current of 4-5 volts at a current density of 0.005 amps per cm A waterclear sorbitol syrup was obtained. The yield was calculated to amount to 95%. The current yield was about What we claim is:

1. The process for the electrolytic reduction of sugars to polyhydric alcohols, comprising the steps of forming an aqueous solution of a reducible sugar and an excess of a water-soluble inorganic sulphite, and submitting the solution having an alkaline reaction to a cathodic reduction in a simple electrolytic cell without a diaphragm, whereby the sulphite is converted into the corresponding sulphate and the anodic oxidation of the obtained reduction products is effectively prevented by maintaining the excess of sulphite in the lectrolyte.

2. Process according to claim 1, in which sodium sulphite is added to the electrolyte.

3. Process according to claim 1, in which ammonium sulphite is added to the electrolyte.

4. Process according to claim 1, including the step of adding to the solution the hydroxide corresponding to the employed sulphite for alkaliz ing the electrolyte.

5. Process according to claim 1, in which glucose is employed as the reducible sugar.

6. Process according to claim 1, in which a purified solution of wood sugar is employed as the reducible sugar.

7. Process according to claim 1, in which a cathode is employed consisting of amalgamated lead.

8. Process according to claim 1, in which a cathode is employed consisting of amalgamated zinc.

HANS RUDOLF HEF'II. WERNER KOLB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,990,582 Creighton Feb. 12, 1935 2,022,894 McAllister Dec. 3, 1935 2,289,189 Hales July 7, 1942 2,458,895 Creighton et al Jan. 11, 1949 

1. THE PROCESS FOR THE ELECTROLYTIC REDUCTION OF SUGARS TO POLYHYDRIC ALCOHOLS, COMPRISING THE STEPS OF FORMING AN AQUEOUS SOLUTION OF A REDUCIBLE SUGAR AND AN EXCESS OF A WATER-SOLUBLE INORGANIC SULPHITE, AND SUBMITTING THE SOLUTION HAVING AN ALKALINE REACTION TO A CATHODIC REDUCTION IN A SIMPLE ELECTROLYTIC CELL WITHOUT A DIAPHRAGM, WHEREBY THE SULPHITE IS CONVERTED INTO THE CORRESPONDING SULPHATE AND THE ANODIC OXIDATION OF THE OBTAINED REDUCTION PRODUCTS IS EFFECTIVELY PREVENTED BY MAINTAINING THE EXCESS OF SULPHITE IN THE ELECTROLYTE. 